Chapter 14 Heat and Temperature: Temperature Energy Transfer Using Heat

Chapter 14

Heat and Temperature:

Temperature

Energy Transfer

Using Heat

TN Standards• CLE 3202.2.3 – Examine the applications and

effects of heat energy

• CLE.3202.2.6 – Investigate the Law of Conservation of Energy

• CLE.3202.TE.3 – Explain the relationship between the properties of a material and the use of the material in the application of a technology

Section 1 - Temperature• Key Questions:

• 1] What does temperature have to do with energy?

• 2] What three temperature scales are commonly used?

• 3] What makes things feel hot or cold?

Temperature and Energy• Kinetic theory of matter

– Matter is made of small particles always moving– Higher temperature, more motion– Large particles move slower

• The temperature of a substance is proportional to the average kinetic energy of the substance’s particles

• All particles have kinetic energy ( atomic )

Measuring Temperature

• As materials are heated, they expand

• Thermometers rely on expansion of liquids– Mercury or Alcohol

• Thermostats rely on expansion of metals

Temperature Scales

• Units: Fahrenheit ( English ) and Celsius ( metric )

• Fahrenheit is English

• Celsius/Kelvin is metric

• Kelvin is an absolute scale– Absolute zero at -273.15 oC

Temperature Scales - Converting

• Celsius Fahrenheit:

TF = 1.8*TC + 32.0

• Fahrenheit Celsius:

TC = ( TF – 32.0 ) / 1.8

Temperature Scales - Converting

• Celsius Kelvin:

TK = TC + 273.15

• Kelvin Celsius:

TC = TK - 273.15

Temperature & Energy Transfer

• When you feel “hot” or “cold” you are detecting a temperature difference

• You are also feeling the affects of energy transfer

• Temperature changes indicate an energy transfer – temperature difference between two objects is felt as heat

• Heat is the energy transferred between objects of different temperature

Section 2 – Heat Transfer• Key Questions:

• 1] How does energy transfer happen?

• 2] What do conductors and insulators do?

• 3] What makes something a good conductor of heat?

Energy Transfer ( Heat Flow )• What is happening in each picture

• Explain how heat is flowing ( ID how heat goes from one object to another )

• What might be happening on the

atomic level?

Different Methods of Transfer

Different Methods of Transfer

• Conduction occurs between objects in direct contact

• Thermal Conduction–heat source is one object

Different Methods of Transfer• Convection results from the movement of

warm fluids ( in contact with heat source )

• Warm fluids rise– Cool when away from heat

• Cool fluids fall

• Convection current –

Path of warm/cool fluids

Different Methods of Transfer• Radiation does not require physical

contact between objects

• Energy transferred as

electromagnetic waves

Conductors & Insulators• A conductor is a material

through which energy can be easily transferred as heat

• An insulator is a material that transfers energy poorly

• Heat energy is transferred through particle collisions

Conductors & Insulators• Heat energy is transferred through

particle collisions

• Gases – poor conductors– Why?

• Denser materials usually are better conductors than less dense

• Metals – very good conductors

• Plastics – poor conductors

Specific Heat• Determines how easily energy

can be transferred as heat

• How much energy is needed to change the temperature of a substance by a certain amount

Specific Heat• Amount of energy needed to raise the

temperature of 1 kg of substance by 1 K

• Energy = specific heat x mass x temp change

• Energy = cmΔT

Specific Heat• Temperature does not change when phases

do; energy goes into phase change - not temperature adjustment

• Latent heat & Heat of Fusion– Gives amount of energy needed for phase change

Heat Flow Conceptual Practice

• Scenarios – Explain what is happening:

• 1] You pick up a coffee cup and it is hot

• 2] You touch a glass of cold SCHAWEET tea

• 3] A breeze makes you shiver

Heat Flow Conceptual Practice

• Which substance can you heat the quickest?

• One with a large or small heat capacity?

Heat Flow Math Practice

• How much energy must be transferred as heat to 200 kg of water ( c = 4,186 J/kg/K ) in a bathtub to raise its temperature from 25 oC to 37 oC?:

Section 3 – Using Heat

• Key Questions:

• 1] What happens to heat energy when it is transferred?

• 2] What do heat engines do?

Thermodynamics

• 1st Law – total energy used in any process is conserved, whether that energy is transferred as work, heat, or both.

Thermodynamics

• 2nd Law – energy transferred as heat ALWAYS moves from higher to lower temperature.

Thermodynamics

• Entropy – randomness or disorder of a system

• Thermo tells us that total entropy of the universe is ALWAYS increasing ( natural tendency )

Heat Engines

Heat Engines